The Stunning Spell (Stupefy), also known as a Stunner or Stupefying Charm[1] is a charm[2] that renders a victim unconscious and halts moving objects. It is commonly used in duels, and was one of the spells Harry Potter taught Dumbledore's Army. If the spell is used by multiple wizards aiming at the same target, the damage it causes is increased, for example; Professor McGonagall had to be moved to St Mungo's after being hit with the spell by multiple Ministry of Magic employees in 1996, and Madam Pomfrey expressed surprise that it did not kill her. If multiple Stunning Spells are aimed at a dragon, they will work, however one alone is not strong enough.[3] It manifests itself as a jet of scarlet light.

The Ministry employees were trying to remove Rubeus Hagrid from Hogwarts, but attacked McGonagall when she offered him protection.[3] The concentrated effects were devastating enough to have her hospitalized, and was considered a miracle that she did not die.

Harry counters unidentified green curses cast by Death Eaters with the Stunning Spell, causing the spells to collide and explode in midair. If these green curses were Killing Curses, then this would indicate that Killing Curse can be parried if it collides with another spell.

It has been implied that Dobby does this to Wormtail in Harry Potter and the Deathly Hallows: Part 1. However, when Harry does this to Umbridge and Mafalda, they are instantly knocked out, while Wormtail stands for a few seconds, says "Ow" (hinting that the spell was quite painful) and collapses. This, as well as his unintended non-reappearance in Part 2, suggests that he may be dead, or that Dobby used a different spell to knock him out.

In Deathly Hallows: Part 2 , Voldemort casts Stupefy at Neville Longbottom out of anger, after Harry Potter seemingly came back to life. Neville was blown backward into the Great Hall, and remained unconscious until he woke to slay Nagini.